Williams argues that the euro has been supported by decent risk appetite along with fundamental developments like the successful long-term refinancing operation. But for now, he told CNBC, "I like buying dollar ZAR."

Williams argues that the South African rand is exposed to a slowdown in China, and that the currency has been moving in tandem with copper prices recently. The rand "is also exposed to higher energy prices, and with oil where it is they're going to start coming under more external pressure."

So much for South Africa - but there's more. "As we see U.S. rates continue to rally" - which should help the dollar - "I think we're going to see a further selloff in emerging market rates as well as in emerging market currencies, for the time being," Williams says.

He wants to enter the trade at 7.6000 with a stop at 7.4500 and a target of 8.0500.